1. Field of the Invention
The present invention relates to a scroll compressor suited for use in, for example, an air conditioner, a refrigerator or the like for business or domestic use.
2. Description of Related Art
Electrically-operated compressors are available in various types including a reciprocating type, a rotary type, a scroll type, and the like, and are widely used in air conditioners, refrigerators and the like. The reciprocating or rotary compressors are characterized by high performance or low cost, while the scroll compressors are characterized by low noise or low vibration. A typical example of the scroll compressors is disclosed in Japanese Laid-open Patent Publication (unexamined) No. 62-168986.
With reference to FIG. 17, the scroll compressor generally comprises a closed vessel 1 and a compression mechanism 4 accommodated within an upper portion of the closed vessel 1. The compression mechanism 4 includes a stationary scroll 2 having a stationary scroll wrap 2a integrally formed therewith and an orbiting scroll 3 having an orbiting scroll wrap 3a integrally formed therewith, with the stationary and orbiting scroll wraps 2a and 3a being in engagement with each other. The orbiting scroll 3 has a shaft 7 integrally formed therewith and journaled in an eccentric bearing 10, which is rectangular in external shape and is in turn accommodated within a recess 9 defined in an upper end portion of a crank shaft 8. An upper portion of the crank shaft 8 is supported by a bearing member 6 with which a thrust bearing 5 is integrally formed to axially support the orbiting scroll 3. The eccentric bearing 10 is allowed to radially move to reduce an orbiting radius of the orbiting scroll 3 but is biased by a leaf spring 11 to maintain the maximum orbiting radius. An electric motor 12 is disposed below the bearing member 6 and is made up of a rotor 13 securely mounted on the crank shaft 8 and a stator 14 rigidly secured to the closed vessel 1 by shrink fitting. The crank shaft 8 is supported by a main bearing 15 and an auxiliary bearing 16 both interposed between it and the bearing member 6, and is driven by the electric motor 12 to cause the orbiting scroll 3 to undergo an orbiting motion relative to the stationary scroll 2.
The closed vessel 1 is provided at its bottom portion with an oil storage portion 18 for storing lubricating oil 17 and at its side portion with a suction pipe 19 rigidly secured thereto for introducing a low-pressure refrigerant thereinto. The closed vessel 1 also accommodates a ring-shaped spacer 20 sealingly welded thereto, below which the pressure of suction gas, i.e., the low-pressure refrigerant acts and above which the pressure of compressed gas, i.e., a high-pressure refrigerant acts. The bearing member 6 has an oil discharge conduit 21 defined therein for discharging the lubricating oil 17 which has lubricated and cooled the main bearing 15, the auxiliary bearing 16, the eccentric bearing 10, and the thrust bearing 5. The bearing member 6 also has a suction hole 29 defined therein through which the low-pressure refrigerant introduced into the closed vessel 1 is supplied to the compression mechanism 4. The stationary scroll 2 and the bearing member 6 are connected to each other via the spacer 20 by means of bolts. The crank shaft 8 has a through-hole 22 defined therein along a longitudinal axis thereof for supplying the main bearing 15, the auxiliary bearing 16, the eccentric bearing 10, and the thrust bearing 5 with the lubricating oil 17 to lubricate and cool them. The crank shaft 8 also has an oil guide 23 mounted on a lower end thereof for sucking up the lubricating oil 17 through the through-hole 22. The closed vessel 1 has a discharge chamber 24 defined therein above the stationary scroll 2.
The scroll compressor shown in FIG. 17 also includes a discharge pipe 25 rigidly secured to the closed vessel 1 for discharging compressed high-pressure refrigerant to the outside of the closed vessel 1, a check valve 26 mounted on the stationary scroll 2 for preventing contrarotation of the orbiting scroll 3 when the scroll compressor is stopped, a valve guide 27 disposed above the check valve 26 and bolted to the stationary scroll 2 for restricting a vertical movement of the check valve 26, and an Oldham ring 28 for preventing the orbiting scroll 3 from rotating about its own axis while permitting it to undergo an orbiting motion relative to the stationary scroll 2.
The scroll compressor of the above-described construction operates as follows.
A low-pressure refrigerant is first introduced into the closed vessel 1 through the suction pipe 19 and then into the compression mechanism 4 through the suction hole 29. An orbiting motion of the orbiting scroll 3 relative to the stationary scroll 2 compresses the low-pressure refrigerant into a high-pressure refrigerant, which is in turn introduced into the discharge chamber 24. The high-pressure refrigerant thus obtained is discharged to the outside of the closed vessel 1 through the discharge pipe 25 to operate a working part. Upon operation of the working part, the high-pressure refrigerant is turned into a low-pressure refrigerant, which is returned back to the suction pipe 19, thus forming a known compression cycle.
On the other hand, lubricating oil 17 sucked up by the oil guide 23 moves upwardly along the through-hole 22 defined in the crank shaft 8, and lubricates and cools the main bearing 15, the auxiliary bearing 16, the eccentric bearing 10, and the thrust bearing 5. Thereafter, the lubricating oil 17 is discharged above the stator 14 through the oil discharge conduit 21 and is eventually returned back to the oil storage portion 18 through a groove 32 defined in the stator 14.
In order to enhance the reliability of the scroll compressor, it is necessary to stop not only generation of a liquid return phenomenon but also that of a liquid compression phenomenon following it. These phenomena are prone to take place in a transient state such as, for example, a process from the starting of the scroll compressor to the time a refrigerating cycle is stabilized, a process during which various operating conditions vary, or the like. The liquid return phenomenon is a phenomenon in which refrigerant turns to a liquid phase, while the liquid compression phenomenon takes place in the compression mechanism 4 and occasionally damages the stationary or orbiting scroll wrap 2a or 3a. A liquid-compression release mechanism is therefore indispensable to positively prevent damage of the stationary and orbiting scroll wraps 2a and 3a.
The liquid-compression release mechanism employed in the conventional scroll compressor is such that when the liquid compression phenomenon takes place, the eccentric bearing 10 is radially inwardly moved to reduce the orbiting radius of the orbiting scroll 3, thereby forming gaps between the stationary and orbiting scroll wraps 2a and 3a to discharge liquid entrapped in crescent-shaped working pockets defined therebetween. During the normal operation, the leaf spring 11 biases the eccentric bearing 10 radially outwardly to maintain the maximum orbiting radius.
However, when the eccentric bearing 10 is moved radially inwardly against a biasing force of the leaf spring 11 to reduce the orbiting radius, it sometimes occurs that the eccentric bearing 10 does not return to its original position but is axially slightly moved towards the orbiting scroll 3. If the operation is continued under a condition in which the eccentric bearing 10 remains at a position shifted toward the orbiting scroll 3, seizing of the eccentric bearing 10 is likely to take place due to a load variation or an inadequate lubrication caused by a change of flow of the lubricating oil, or an undesired contact of one end of the eccentric bearing 10 with an associated end of the orbiting scroll 3 is likely to generate abnormal noise or cause seizing, thus adversely affecting the reliability of the scroll compressor.
If the biasing force of the leaf spring 11 is strengthened to prevent an axial movement of the eccentric bearing 10, the problem arises that an undesired deformation of the eccentric bearing 10 reduces a clearance between the shaft 7 and the eccentric bearing 10 and subsequently causes seizing of the eccentric bearing 10. In order to avoid deformation of the eccentric bearing 10, if it is rigidified to have an increased physical strength, the weight and size thereof is increased, resulting in an increase in size of the scroll compressor.